New strain of mad cow disease is closer to human form

Italian scientists have found a potential second form of mad cow disease that more closely resembles the human Creutzfeldt-Jakob disease than does the usual cow form of the illness.

The brain-wasting diseases BSE, known as mad cow disease, and human CJD are caused by different forms of mutant proteins called prions. More than 150 people, mainly in Britain, have contracted variant CJD, a fatal brain disease believed to be acquired by eating meat from BSE-infected cows.

The Italian researchers report that a study of eight cows with mad cow disease found two had brain damage resembling that in the human victims of CJD.

They said the cows were infected with prions that resembled those involved in the standard form of the human disease, called sporadic CJD, not the variant caused by eating infected meat.

Salvatore Monaco, who headed the new study, said the findings may indicate that cattle can also develop a sporadic form of the disease, but it might also be a new food-borne form of the illness.

Paul Brown of the National Institutes of Health in the US said the finding does not indicate an increased threat to humans. If a new form of the disease were affecting humans, there should be an increase in the incidence of CJD, said Dr Brown, who was not part of the research team.

However, scientists in Europe have studied all cases of sporadic CJD for the past decade and the incidence has not changed, said Dr Brown, an expert in the disease who works at the US National Institute of Neurological Disease and Stroke.

The human and cattle diseases cause holes to form in the brain. The Italian researchers found that, in addition to the holes, two cows had an accumulation of amyloid plaque in their brains.

Amyloid plaques are an indication of Alzheimer's disease in humans. They have also been found in people with sporadic CJD but had not previously been found in cattle, the researchers said.

The Italians have named the new form of mad cow disease with amyloid plaques BASE.

"Although observed in only two cattle, the BASE phenotype could be more common than expected," they reported.

Dr Monaco, of the department of neurological and visual science, Policlinico GB Rossi, in Verona, said he believes the incidence could be as high as 5 per cent among cattle with mad cow symptoms.

But while human CJD and BASE share several characteristics, the Italian researchers cautioned against assuming a link between the two.

The findings of the team led by Dr Monaco, are reported in this week's online edition of Proceedings of the National Academy of Science.